Everything that we humans eat or drink is either metabolized by the body or excreted from it. Because black coffee is free of calories we may be forgiven for assuming that how the body metabolizes coffee is not important but there is more to the story.

Caffeine Metabolism

The part of coffee that wakes us up and keeps us going is caffeine. It is broken down or metabolized in the liver taking away about eighty-seven percent of what is taken in. The remainder goes to the kidneys and is passed out of the body with urine. When caffeine is metabolized the primary product is paraxanthine which, like caffeine, is a central nervous system stimulant. Paraxanthine has a half life of about three hours as it is also metabolized. While paraxanthine is responsible for much of the stimulant effect of coffee its own metabolites are not.

Paraxanthine

Paraxanthine is an antagonist of adenosine receptors. Because adenosine causes relaxation and sleepiness, paraxanthine helps keep us stay awake. Paraxanthine not only causes wakefulness but also improves thinking or cognitive function and blood circulation in the brain. It is a strong contributor to the improved physical performance and motor function seen in coffee drinkers. Unlike caffeine, paraxanthine does not cause as much blood pressure elevation or speeding up of the heart. Paraxanthine causes less anxiety than caffeine.

Coffee Antioxidant Metabolism

Antioxidants are largely responsible for the many health benefits obtained from drinking coffee. Antioxidants are primarily metabolized in the liver where many of the metabolic byproducts have more antioxidant properties than the original compounds. Because metabolism of antioxidants happens quickly they do not stay around in the blood stream for very long. However, both the liver and kidneys store antioxidants leading to longer term protective benefits. Antioxidants are not totally metabolized. A portion is excreted in the urine and also via sweating.

Caffeine in Coffee Affects Metabolism

While the constituents of coffee are metabolized, one of them, caffeine, has a direct affect on the rate of metabolism. Caffeine increases the rate of metabolism in the body by up to eight percent for up to three hours before it itself is metabolized. Paraxanthine, the primary metabolic product of caffeine also speeds up metabolism. Both paraxanthine and caffeine do this by central nervous system stimulation. Caffeine helps promote thermogenesis, which is the sum total of processes that turn food into energy in the human body.

What Else in Your Cup of Coffee Gets Metabolized?

While black coffee is free of calories many people add milk, cream, or sugar to their Java. Your local neighborhood coffee shop probably has flavored lattes, etc. Thus coffee metabolism also involves breaking down caloric coffee ingredients. Simple sugars are metabolized in two or three hours while complex carbohydrates take somewhat longer. Metabolism of fats that may come with your coffee can take hours or even days. While excessive consumption of fats in your diet can lead to obesity there may be a benefit as well. A common effect to adding too much sugar to your black coffee is rebound hypoglycemia where the body secretes insulin and rapidly drops the blood sugar level often causing sweating, anxiety, trembling, lightheadedness, and even confusion, trouble concentrating, mood changes and irritability. A common response is to drink more coffee with sugar which quickly reverses those symptoms only to start the cycle all over again. Thus, adding whole milk of cream along with sugar to your coffee prolonging metabolism can help prevent the rebound hypoglycemia cycle.